1. Technical Field
The present invention generally relates to a lithography process and a fabrication process using the lithography process and, more particularly, to a lithography process which utilizes one or more anti-reflective coating films and a fabrication process using the lithography process.
2. Description of the Related Art
In the fabrication of semiconductor integrated circuits such as semiconductor memory devices, optical photofabrication techniques may be used to provide desired patterns for circuit features. These techniques typically involve the controlled projection of actinic light (e.g., ultraviolet (UV) or deep ultraviolet (DUV) radiation) in order to transfer a pattern from a photolithographic mask onto a layer of light-sensitive material such as a resist deposited on a substrate. The mask typically embodies a light transmissive substrate with a layer of light blocking material defining the patterns of circuit features to be transferred to the resist coated substrate. If a negative resist is used, then the projected exposure light passing through the mask will cause the exposed areas of the resist layer to undergo polymerization and cross-linking, resulting in an increased molecular weight. In a subsequent development step, unexposed portions of the resist layer will wash off with the developer, leaving a pattern of resist material constituting a reverse or negative image of the mask pattern. Alternatively, if a positive resist is used, the exposure light passing through the mask will cause the exposed portions of the resist layer to become soluble to the developer, such that the exposed resist layer portions will wash away in the development step, leaving a pattern of resist material corresponding directly to the mask pattern. In both cases, the remaining resist will serve to define a pattern of exposed material that will undergo subsequent fabrication steps (e.g., etching and deposition) for forming the desired semiconductor devices. The exposed material may, for example, be an insulator, a conductor, or a semiconductor.
One problem which occurs in lithography processes is that light is reflected back into the resist from the underlying substrate. This problem is particularly acute in lithography processes for fabricating non-planar substrates. These reflections can cause unwanted exposure of the resist, thereby degrading the pattern transfer process. In order to reduce such reflections, a so-called antireflective coating (ARC) film may be applied and baked on the substrate to be fabricated prior to forming the resist. After the resist is applied, patterns are resolved in the resist by exposure light and the patterns are transferred to both the ARC film and the substrate to be fabricated by an etching process such as reactive ion etching (RIE). After the pattern transfer, both the resist and the ARC film are removed. While the use of an ARC film improves the pattern transfer process, the application and removal of the ARC film complicates an overall manufacturing process which includes many separate pattern transfer processes. In addition, in processes such as a dual damascene process, it can be necessary to apply the ARC film to a surface having openings formed therein. The application and complete removal of an ARC film in this situation can be difficult, thereby further complicating the overall fabrication process. Still further, while an antireflective coating film improves the pattern transfer process in terms of reducing reflections, critical dimension bias after the ARC film etching must be taken into account. Thus, it is desirable that the ARC film would be as thin as possible.
Thus, it would be desirable to provide a lithography process which overcomes these and other problems associated with conventional ARC films.